In the operation of producing oil wells, it is necessary from time to time to remove devices from the well. An overshot is normally used for this service. The overshot is normally lowered into the well on a wireline. It is lowered and set down on the item to be lifted or removed. As it is lowered, the overshot surrounds the upper end of the fish to be moved in the well. The fish may be equipped with a conventional or API standard fishing neck. The device of the present invention also will grasp and lift a cylindrical object or the like. In other words, it is able to grasp the exterior of a solid rod or tubular pipe. In any case, it engages the fish and accommodates a variety of shapes.
Occasionally, the fish will be stuck. When a strain is taken on the wireline, it will be determined that the wireline is unable to lift the fish because the fish is stuck for some unknown reason. As a lifting force is applied, it is increased until the breaking point of the wireline is approached. At this juncture if the fish cannot be retrieved, it is necessary to leave the fish in location and retrieve the overshot. In such a circumstance, the present invention comes into play. It incorporates a means which enables a jar to be tripped against the wireline tool. The jar impacts on the overshot. It drives the parts of the overshot in telescoping fashion to a point where the fish is released by the grapple which engages it. Moreover, the overshot incorporates a pin which is sheared intentionally on jarring movement. The jarring movement shears the pin and simultaneously locks the grapple in its most relaxed or released position. When this occurs, the grapple will release anything which is held by it.
This of course avoids lodging the overshot tool in the well attached to the fish, thereby compounding the problem of retrieving the stuck fish. The present invention thus defines an overshot which grasps a fish with a grapple which uses wedging action with the fingers of the grapple to engage the fish and yet which further includes a means enabling the overshot to be disengaged should this be necessary. The jarring movement can be routinely achieved through the use of a jar mechanism, a device readily available.